In this paper we address the challenges that arise due to heterogeneities across independently created and autonomously managed Web service requesters and Web service providers. Previous work in this area either involved significant human effort or in cases of the efforts seeking to provide largely automated approaches, overlooked the problem of data heterogeneities, resulting in partial solutions that would not support executable workflow for real-world problems. In this paper, we present a planning-based approach to solve both the process heterogeneity and data heterogeneity problems. We adopt a declarative approach to capture the partner specifications external to the process and demonstrate the usefulness of this approach in adding more dynamism to Web processes. Our system successfully outputs a BPEL file which correctly solves a non-trivial real-world problem in the SWS Challenge.